An instrument has been developed to use absorption of radiation for the on-line determination of the concentration of contaminants such as nitrate ions, ammonia and organic matter which are indicative of the extent of pollution occurring in a wide range of natural and processed waters.
UV spectroscopy can be utilized for the determination of most organic and certain non-organic compounds (e.g. chlorine) using simple techniques. This method relies on the absorption of light in a more restricted band than the visible i.e. from 180 to 400 nm. Many elements absorb ultra-violet light selectively in the band from 200 to 300 nm, each at a specific wavelength. The absorption peak profile is wide since it results from absorption from different origins, mainly due to electronic transitions on to which vibrations, rotations and translation are superimposed. As a consequence, characterization of the sensing wavelength is not very specific. It is not always possible to provide light of adequate intensity at the wavelength of peak absorption. Hence an adjacent wavelength must be used, even though it reduces the sensitivity somewhat. Another alternative which is more complex and costly would be the use of a grating system to provide any particular wavelength and deconvoluting the spectra obtained. However, in the simple system chosen, deviations from the peak absorption wavelength do not give rise to major difficulties.
According to the present invention there is provided an apparatus for measuring the level of a contaminant in a fluid comprising a measuring chamber, a first source of optical radiation of a predetermined wavelength adapted to direct the radiation through the chamber, detector means to detect the radiation after passage through the measuring chamber, pump means to urge a test fluid test from a fluid source to the measuring chamber, fluid processing means positioned between the fluid source and the measuring chamber to process the fluid to change an optical effect of the contaminant, bypass means to bypass the fluid processing means and valve means alternately to direct the fluid to the processing means and the bypass means.